mwrap 2.2.0

This release adds Ruby 2.7, 3.0, and 3.1 support.

This also fixes breakage in urcu v0.11.4, v0.12.3, and v0.13.1.
While urcu v0.12.4 and v0.13.2 were released 2022-08-18,
old versions will continue to be in distros for a while
(and urcu v0.11.x won't be updated).

There are also several updates ported from the Perl version.

7 changes since v2.1.0 in 2018:
      memalign: perform rcu_read_unlock on ENOMEM
      workaround breakage from urcu v0.11.4
      constify arg for totals_add_rcu
      support Ruby 3.0.x
      disable HeapPageBody count test for Ruby 3.1
      quiet uninitialized and unused variable warnings
      various doc updates